The occurrence of called "arcing faults" within industrial and residential establishments has resulted in a large number of patents and publications relating to the nature of the arcing faults and how to determine its occurrence.
The higher frequency conditions that occur with the arcing faults, lends to isolating the higher frequency harmonics and comparing the harmonics to reference harmonic values indicative of an arcing fault.
U.S. Pat. No. 5,602,709 entitled "High Impedance Fault Detector" describes one such means for detecting arcing fault occurrence.
U.S. Pat. No. 5,561,605 entitled "Arc Detection Using Current Variation" teaches arcing fault detection by sampling line current with a harmonic notch filter. U.S. Pat. No. 4,466,071 entitled "High Impedance Fault Detection Apparatus and Method describes the prevalence of even harmonics within the arcing fault frequency pattern.
Arcing currents, viewed in the frequency domain, have elements of the fundamental frequency, even harmonics and odd harmonics of the fundamental. Many non-linear loads such as light dimmers, computers, and dc supplies show fundamental and odd harmonics, but tend not to have even harmonics.
Measurement of such even harmonics therefore provides an effective, selective means of detecting arcing in power line current. Conventional techniques for even harmonic measurement employ digital signal processing computers and sampled data systems that may be overly expensive for residential application. Discrete Fourier Transforms or Fast Fourier Transforms are required for separating the odd harmonics from the electrical signal. A description of one approach to even harmonic measurement is found in IEEE Transactions on Power Delivery, Vol. 6, No. 2, April 1991 entitled "High Impedance Fault Detection Utilizing Incremental Variance of Normalized Even Order Harmonic Power"
U.S. Pat. No. 5,659,453 entitled "Arc Burst Pattern Analysis Fault Detection System" describes a circuit arrangement for analyzing half cycles of the fundamental current to determine whether arcing faults may be present.
One purpose of the instant invention is to describe an economical approach to arcing fault detection that does not require complex electronic filters and the like to detect the presence of such even harmonics and the absence of odd harmonics for arcing fault determination.